The nine-day exercise is aimed at testing the military contribution to the overall security effort and is putting airmen, soldiers and sailors through their paces in the skies over the South East.

It includes the use of the Typhoon fighters which arrived at RAF Northolt yesterday, Army Lynx helicopters and Royal Navy Sea King ASaC (Airborne Surveillance and Control) helicopters. The air defence missile systems testing follows several months of engagement with the areas where they are due to be located during the Olympics.

This included extensive talks with local authorities and landowners, briefing local MPs, discussions with community representatives, and, most recently, delivering leaflets to residents' homes.

Defence Secretary Philip Hammond said:

"Whilst there is no reported threat to the London Olympics, the public expects that we have in place a range of measures aimed at ensuring the safety of this once-in-a-generation event.

"As part of the comprehensive security plan being tested this week, ground-based air defence systems are temporarily at locations across London.

"We believe they will reassure the public and those attending the Games, while providing a powerful deterrent.

"Although a process of engagement has been underway for four months, involving community leaders, local authorities, local MPs and landowners, final decisions have yet to be taken."

At a media facility today at Blackheath, both the Rapier system and the smaller high velocity missile (HVM) system were on show, with military personnel on hand to answer technical questions in the same way as they have at meetings with residents held this week.

While a formal government decision on whether the equipment will be sited during the Games themselves is yet to be made, the proposed deployment would see the two different types of missile systems in use as part of a broad array of other defence capabilities.

The primary form of air defence will be provided by RAF Typhoon aircraft which will form the outer ring of defence outside London. They will be assisted by Royal Navy Lynx and RAF Puma helicopters armed with snipers, with ground-based air defence systems forming the final line of defence.